Polymerization processes for alpha-olefin/propylene copolymers

ABSTRACT

Improved thermoplastic polymer blend compositions comprising an isotactic polypropylene component and an alpha-olefin and propylene copolymer component, said copolymer comprising crystallizable alpha-olefin sequences. In a preferred embodiment, improved thermoplastic polymer blends are provided comprising from about 35% to about 85% isotactic polypropylene and from about 30% to about 70% of an ethylene and propylene copolymer, wherein said copolymer comprises isotactically crystallizable propylene sequences and is predominately propylene. The resultant blends manifest unexpected compatibility characteristics, increased tensile strength, and improved process characteristics, e.g., a single melting point.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Ser. No. 10/613,373, filed Jul. 3,2003 which is a divisional of Ser. No. 08/910,001, filed Aug. 12, 1997,now U.S. Pat. No. 6,635,715, the disclosures of which are incorporatedby reference in their entireties.

FIELD OF THE INVENTION

The invention relates to polymer blends of at least two polymers havingsurprising properties when compared to the properties of the individualpolymers prior to blending. More specifically, the invention relates toblends of thermoplastic polymers, e.g., according to one embodiment,isotactic polypropylene and an olefin copolymer. The invention furtherrelates to thermoplastic polymer blends comprising isotacticpolypropylene and, according to one embodiment, a copolymer of ethyleneand propylene, wherein the copolymer comprises isotacticallycrystallizable alpha-olefin sequences. In addition, the inventionrelates to methods for making the above polymers and blends thereof.

BACKGROUND OF THE INVENTION

Although blends of isotactic polypropylene and ethylene propylene rubberare well known in the prior art, prior art Ziegler-Natta catalystsystems could only produce ethylene propylene rubber compositions withgreater than 30% by weight ethylene at practical, economicpolymerization conditions. There exists a need for polymeric materialswhich have advantageous processing characteristics while still providingsuitable end properties to articles formed therefrom, e.g., tensile andimpact strength. Copolymers and blends of polymers have been developedto try and meet the above needs. U.S. Pat. No. 3,882,197 to Fritz et al.describes blends of stereoregular propylene/alpha-olefin copolymers,stereoregular propylene, and ethylene copolymer rubbers. In U.S. Pat.No. 3,888,949 Chi-Kai Shih, assigned to E I DuPont, shows the synthesisof blend compositions containing isotactic polypropylene and copolymersof propylene and an alpha-olefin, containing between 6–20 carbon atoms,which have improved elongation and tensile strength over either thecopolymer or isotactic polypropylene. Copolymers of propylene andalpha-olefin are described wherein the alpha-olefin is hexene, octene ordodecene. However, the copolymer is made with a heterogeneous titaniumcatalyst which makes copolymers which are non-uniform in compositionaldistribution and typically broad in molecular weight distribution.Compositional distribution is a property of copolymers where thereexists statistically significant intermolecular or intramoleculardifference in the composition of the polymer. Methods for measuringcompositional distribution are described later. The presence ofintramolecular compositional distribution is described in U.S. Pat. No.3,888,949 by the use of the term “block” in the description of thepolymer where the copolymer is described as having “sequences ofdifferent alpha-olefin content.” Within the context of the inventiondescribed above the term sequences describes a number of olefin monomerresidues catenated together by chemical bonds and obtained by apolymerization procedure.

In U.S. Pat. No. 4,461,872, A. C. L. Su improved on the properties ofthe blends described in U.S. Pat. No. 3,888,949 by using anotherheterogeneous catalyst system. However, the properties and compositionsof the copolymer with respect to either the nature and type of monomers(alpha-olefin containing 6–20 carbon atoms) or the blocky heterogeneousintra/inter molecular distribution of the alpha-olefin in the polymerhave not been resolved since the catalysts used for these polymerizationof propylene and alpha-olefin are expected to form copolymers which havestatistically significant intermolecular and intramolecularcompositional differences.

In two successive publications in the journal of Macromolecules, 1989,V22, pages 3851–3866, J. W. Collette of E. I. DuPont has describedblends of isotactic polypropylene and partially atactic polypropylenewhich have desirable tensile elongation properties. However, thepartially atactic propylene has a broad molecular weight distribution asshown in FIG. 8 of the first publication. The partially atacticpolypropylene is also composed of several fractions, which differ in thelevel of tacticity of the propylene units as shown by the differences inthe solubility in different solvents. This is shown by the correspondingphysical decomposition of the blend which is separated by extractionwith different solvents to yield individual components of uniformsolubility characteristics as shown in Table IV of the abovepublications.

In U.S. Pat. Nos. 3,853,969 and 3,378,606, E. G. Kontos discloses theformation of in situ blends of isotactic polypropylene and “stereoblock” copolymers of propylene and another olefin of 2 to 12 carbonatoms, including ethylene and hexene. The copolymers of this inventionare necessarily heterogeneous in intermolecular and intramolecularcomposition distribution. This is demonstrated by the synthesisprocedures of these copolymers which involve sequential injection ofmonomer mixtures of different compositions to synthesize polymericportions of analogously different compositions. In addition, FIG. 1 ofboth patents shows that the “stereo block” character, which is intra orintermolecular compositional differences in the context of thedescription of the present invention, is essential to the benefit of thetensile and elongation properties of the blend. In situ blends ofisotactic polypropylene and compositionally uniform random ethylenepropylene copolymers have poor properties. Moreover, all of thesecompositions either do not meet all of the desired properties forvarious applications, and/or involve costly and burdensome process stepsto achieve the desired results.

Similar results are anticipated by R. Holzer and K. Mehnert in U.S. Pat.No. 3,262,992 assigned to Hercules wherein the authors disclose that theaddition of a stereoblock copolymer of ethylene and propylene toisotactic polypropylene leads to improved mechanical properties of theblend compared to isotactic polypropylene alone. However, these benefitsare described only for the stereoblock copolymers of ethylene andpropylene. The synthesis of the these copolymers is designed aroundpolymerization conditions where the polymer chains are generated indifferent compositions of ethylene and propylene achieved by changing,with time, the monomer concentrations in the reactor. This is shown inexamples 1 and 2. The stereoblock character of the polymer isgraphically shown in the molecular description (column 2, line 65) andcontrasted with the undesirable random copolymer (column 2, line 60).The presence of stereoblock character in these polymers is shown by thehigh melting point of these polymers, which is much greater than themelting point of the second polymer component in the present invention,shown in Table 1, as well as the poor solubility of these hetero blockmaterials, as a function of the ethylene wt % of the material as shownin Table 3.

It would be desirable to produce a blend of a crystalline polymer,hereinafter referred to as the “first polymer component,” and acrystallizable polymer, hereinafter referred to as the “second polymercomponent”, having advantageous processing characteristics while stillproviding end products made from the blend composition having thedesired properties, i.e., increased tensile strength, elongation, andoverall toughness. The first polymer component (abbreviated as “FPC” inthe Tables below) and the second polymer component (abbreviated as “SPC”in the Tables below). Indeed, there is a need for an entirely polyolefincomposition which is thermally stable, heat resistant, light resistantand generally suitable for thermoplastic elastomer (TPE) applicationswhich has advantageous processing characteristics. Such an entirelypolyolefin composition would be most beneficial if the combination ofthe first polymer component and the second polymer component weresignificantly different in mechanical properties than thecompositionally weighted average of the corresponding properties offirst polymer component and second polymer component alone. Weanticipate, while not meant to be limited thereby, that the potency ofthe second polymer component may be increased if it only consists of oneor two polyolefin copolymers material defined by uniform intramolecularand intermolecular composition and microstructure.

The term “crystalline,” as used herein for first polymer component,characterizes those polymers which possess high degrees of inter- andintra-molecular order, and which melt higher than 110° C. and preferablyhigher than 115° C. and have a heat of fusion of at least 75 J/g, asdetermined by DSC analysis. And, the term “crystallizable,” as usedherein for second polymer component, describes those polymers orsequences which are mainly amorphous in the undeformed state, but uponstretching or annealing, crystallization occurs. Crystallization mayalso occur in the presence of the crystalline polymer such as firstpolymer component. These polymers have a melting point of less than 105°C. or preferably less than 100° C. and a heat of fusion of less than 75J/g as determined by DSC.

SUMMARY OF THE INVENTION

The present invention, according to one embodiment, is directed to theuse of chiral metallocene catalysts to (1) readily produce secondpolymer component being ethylene propylene rubber compositions withabout 4 wt % to about 25 wt % ethylene, and (2) readily produce secondpolymer component compositions containing isotactic propylene sequenceslong enough to crystallize. Thus, the invention is directed, accordingto one embodiment, to semicrystalline materials (second polymercomponent), which when blended with isotactic polymers (first polymercomponent), show an increased level of compatibility between theethylene propylene and isotactic polypropylene phases. While not meantto be limited thereby, we believe the increased compatibility is due tothe similarity of the composition of the first polymer component and allof the second polymer component. Thus, the uniformity of the intra- andinter-molecular composition of the second polymer component is ofimportance. In particular, it is important that substantially all of thecomponents of the second polymer component be within the narrowcomposition range of ethylene and propylene defined above. In addition,the presence of isotactic propylene sequences in the second polymercomponent is of benefit for the improved adhesion of the domains of thefirst polymer component and the second polymer component in the polymerblend composition. As a result, blends of isotactic polypropylene withethylene propylene copolymers according to the invention, have improvedphysical properties as compared to isotactic polypropylene blends withprior art ethylene propylene rubbers.

According to one embodiment, a composition of the present inventioncomprises a blend of at least a first polymer component and a secondpolymer component. The blend comprises greater than about 2% by weightof the first polymer component comprising an alpha-olefin propylenecopolymer containing isotactic polypropylene crystallinity with amelting point of about 115° C. to about 170° C. The blend also containsa second polymer component comprising a copolymer of propylene and atleast one other alpha-olefin having less than 6 carbon atoms, andpreferably 2 carbon atoms. The second polymer component copolymer of theinvention, according to one embodiment, comprises isotacticallycrystallizable propylene sequences and greater than 75% by weightpropylene and preferably greater than 80% by weight propylene.

According to another embodiment, a thermoplastic polymer blendcomposition of the invention comprises a first polymer component and asecond polymer component. The first polymer component comprisesisotactic polypropylene, and is present in an amount of about 2% toabout 95% by weight and more preferably 2% to 70% by weight of the totalweight of the blend. The first polymer component may also be comprisedof commonly available isotactic polypropylene compositions referred toas impact copolymer or reactor copolymer. However these variations inthe identity of the first polymer component are acceptable in the blendonly to the extent that all of the components of the first polymercomponent are substantially similar in composition and the first polymercomponent is within the limitations of the crystallinity and meltingpoint indicated above. This first polymer component may also containadditives such as flow improvers, nucleators and antioxidants which arenormally added to isotactic polypropylene to improve or retainproperties. All of these polymers are referred to as the first polymercomponent.

The second polymer component is a thermoplastic comprising a randomcopolymer of ethylene and propylene having a melting point by DSC of 25°C. to 105° C., preferably in the range 25° C. to 90° C., more preferablyin the range of 40° C. to 90° C. and an average propylene content byweight of at least 75% and more preferably at least 80%. The secondpolymer component is made with a polymerization catalyst which formsessentially or substantially isotactic polypropylene, when all orsubstantially all propylene sequences in the second polymer componentare arranged isotactically. This copolymer contains crystallizablepropylene sequences due to the isotactic polypropylene. The secondpolymer component is statistically random in the distribution of theethylene and propylene residues along the chain. Quantitative evaluationof the randomness of the distribution of the ethylene and propylenesequences may be obtained by consideration of the experimentallydetermined reactivity ratios of the second polymer component. We believethat the second polymer component is random in the distribution ofethylene and propylene sequences since (1) it is made with a singlesited metallocene catalyst which allows only a single statistical modeof addition of ethylene and propylene and (2) it is made in a wellmixed, continuous monomer feed stirred tank polymerization reactor whichallows only a single polymerization environment for substantially all ofthe polymer chains of the second polymer component. Thus there issubstantially no statistically significant difference in the compositionof the second polymer component either among two polymer chains or alongany one chain.

The ratio of the first polymer component to the second polymer componentof the blend composition of the present invention may vary in the rangeof 2:98 to 95:5 by weight and more preferably in the range 2:98 to 70:30by weight.

According to another embodiment of the present invention, the secondpolymer component may contain small quantities of a non-conjugated dieneto aid in the vulcanization and other chemical modification of the blendof the first polymer component and the second polymer component. Theamount of diene is limited to be no greater than 10 wt % and preferablyno greater than 5 wt %. The diene may be selected from the groupconsisting of those which are used for the vulcanization of ethylenepropylene rubbers and preferably ethyldiene norbornene, vinyl norborneneand dicyclopentadiene.

According to still a further embodiment, the invention is directed to aprocess for preparing thermoplastic polymer blend compositions. Theprocess comprises: (a) polymerizing propylene or a mixture of propyleneand one or more monomers selected from C₂ or C₄–C₁₀ alpha olefins in thepresence of a polymerization catalyst wherein a substantially isotacticpropylene polymer containing at least about 90% by weight polymerizedpropylene is obtained; (b) polymerizing a mixture of ethylene andpropylene in the presence of a chiral metallocene catalyst, wherein acopolymer of ethylene and propylene is obtained comprising up to about25% by weight ethylene and preferably up to 20% by weight ethylene andcontaining isotactically crystallizable propylene sequences; and (c)blending the propylene polymer of step (a) with the copolymer of step(b) to form a blend.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The blend compositions of the present invention generally are comprisedof two components: (1) a first polymer component comprising isotacticpolypropylene, and (2) a second polymer component comprising analpha-olefin (other than propylene) and propylene copolymer.

The First Polymer Component (FPC)

In accordance with the present invention, the first thermoplasticpolymer component (first polymer component), i.e., the polypropylenepolymer component may be homopolypropylene, or copolymers of propylene,or some blends thereof. The polypropylene used in the present blends canvary widely in form. For example, substantially isotactic polypropylenehomopolymer can be used or the polypropylene can be in the form of acopolymer containing equal to or less than about 10 weight percent ofother monomer, i.e., at least about 90% by weight propylene. Further,the polypropylene can be present in the form of a graft or blockcopolymer, in which the blocks of polypropylene have substantially thesame stereoregularity as the propylene-alpha-olefin copolymer, so longas the graft or block copolymer has a sharp melting point above about110° C. and preferably above 115° C. and more preferably above 130° C.,characteristic of the stereoregular propylene sequences. The firstpolymer component of the present invention is predominately crystalline,i.e., it has a melting point generally greater than about 110° C.,preferably greater than about 115° C., and most preferably greater thanabout 130° C. The propylene polymer component may be a combination ofhomopolypropylene, and/or random, and/or block copolymers as describedherein. When the above propylene polymer component is a randomcopolymer, the percentage of the copolymerized alpha-olefin in thecopolymer is, in general, up to about 9% by weight, preferably about 2%to about 8% by weight, most preferably about 2% to about 6% by weight.The preferred alpha-olefins contain 2 or from 4 to about 12 carbonatoms. The most preferred alpha-olefin is ethylene. One, or two or morealpha-olefins can be copolymerized with propylene.

Exemplary alpha-olefins may be selected from the group consisting ofethylene; butene-1; pentene-1,2-methylpentene-1,3-methylbutene-1;hexene-1,3-methylpentene-1,4-methylpentene-1,3,3-dimethylbutene-1;heptene-1; hexene-1; methylhexene-1; dimethylpentene-1trimethylbutene-1; ethylpentene-1; octene-1; methylpentene-1;dimethylhexene-1; trimethylpentene-1; ethylhexene-1;methylethylpentene-1; diethylbutene-1; propylpentane-1; decene-1;methylnonene-1; nonene-1; dimethyloctene-1; trimethylheptene-1;ethyloctene-1; methylethylbutene-1; diethylhexene-1; dodecene-1 andhexadodecene-1.

The thermoplastic polymer blend compositions of the present inventionmay comprise from about 2% to about 95% by weight of first polymercomponent. According to a preferred embodiment, the thermoplasticpolymer blend composition of the present invention may comprise fromabout 2% to about 70% by weight of the first polymer component.According to the most preferred embodiment, the compositions of thepresent invention may comprise from about 5% to about 70% by weight ofthe first polymer component.

There is no particular limitation on the method for preparing thispropylene polymer component of the invention. However, in general, thepolymer is a propylene homopolymer obtained by homopolymerization ofpropylene in a single stage or multiple stage reactor. Copolymers may beobtained by copolymerizing propylene and an alpha-olefin having 2 orfrom 4 to about 20 carbon atoms, preferably ethylene, in a single stageor multiple stage reactor. Polymerization methods include high pressure,slurry, gas, bulk, or solution phase, or a combination thereof, using atraditional Ziegler-Natta catalyst or a single-site, metallocenecatalyst system. The catalyst used is preferably one which has a highisospecificity. Polymerization may be carried out by a continuous orbatch process and may include use of chain transfer agents, scavengers,or other such additives as deemed applicable.

The Second Polymer Component (SPC)

The second polymer component of the polymer blend compositions of thepresent invention comprises a copolymer of propylene and anotheralpha-olefin having less than 6 carbon atoms, preferably ethylene.Optionally, the second component of the composition of the presentinvention may further comprise, in addition to the above mentioned,amounts of a diene. The second polymer component of the presentinventive composition preferably, according to one embodiment, comprisesa random copolymer having a narrow compositional distribution. While notmeant to be limited thereby, it is believed that the narrow compositiondistribution of the second polymer component is important. Theintermolecular composition distribution of the polymer is determined bythermal fractionation in a solvent. A typical solvent is a saturatedhydrocarbon such as hexane or heptane. This thermal fractionationprocedure is described below. Typically, approximately 75% by weight andmore preferably 85% by weight of the polymer is isolated as a one or twoadjacent, soluble fraction with the balance of the polymer inimmediately preceding or succeeding fractions. Each of these fractionshas a composition (wt % ethylene content) with a difference of nogreater than 20 wt. % (relative) and more preferably 10 wt % (relative)of the average wt % ethylene content of the whole second polymercomponent. The second polymer component is narrow in compositionaldistribution if it meets the fractionation test outlined above.

In all second polymer component, the number and distribution of ethyleneresidues is consistent with the random statistical polymerization ofethylene, propylene and optional amounts of diene. In stereoblockstructures, the number of monomer residues of any one kind adjacent toone another is greater than predicted from a statistical distribution inrandom copolymers with a similar composition. Historical polymers withstereoblock structure have a distribution of ethylene residuesconsistent with these blocky structures rather than a random statisticaldistribution of the monomer residues in the polymer. The intramolecularcomposition distribution of the polymer may be determined by C-13 NMRwhich locates the ethylene residues in relation to the neighboringpropylene residue. A more practical and consistent evaluation of therandomness of the distribution of the ethylene and propylene sequencesmay be obtained by the following consideration. We believe that thesecond polymer component is random in the distribution of ethylene andpropylene sequences since (1) it is made with a single sited metallocenecatalyst which allows only a single statistical mode of addition ofethylene and propylene and (2) it is made in a well mixed, continuousmonomer feed stirred tank polymerization reactor which allows only asingle polymerization environment for substantially all of the polymerchains of the second polymer component.

The second polymer component preferably, according to one embodiment ofthe invention, has a single melting point. The melting point isdetermined by DSC. Generally, the copolymer second component of thepresent invention has a melting point below the first polymer componentof the blend typically between about 105° C. and 25° C. Preferably, themelting point of second polymer component is between about 90° C. and25° C. Most preferably, according to one embodiment of the presentinvention, the melting point of the second polymer component of thecomposition of the present invention is between 90° C. and 40° C.

The second polymer component preferably has a narrow molecular weightdistribution (MWD) between about 1.8 to about 5.0, with a MWD betweenabout 2.0 to about 3.2 preferred.

The second polymer component of the present inventive compositioncomprises isotactically crystallizable alpha-olefin sequences, e.g.,preferably propylene sequences (NMR). The crystallinity of the secondpolymer component is, preferably, according to one embodiment, fromabout 2% to about 65% of homoisotactic polypropylene, preferably between5% to 40%, as measured by the heat of fusion of annealed samples of thepolymer.

According to another embodiment of the present invention, the secondpolymer component of the composition comprises from about 5% to about25% by weight alpha-olefin, preferably from about 6% to about 20% byweight alpha-olefin, and most preferably, it comprises from about 6% toabout 18% by weight alpha-olefin and even more preferably between 10% to16% by alpha-olefin. These composition ranges for the second polymercomponent are dictated by the object of the present invention. Atalpha-olefin compositions lower than the above lower limits for thesecond polymer component, the blends of the first polymer component andsecond polymer component are hard and do not have the favorableelongation properties of the blends of the present invention. Atalpha-olefin compositions higher than the above higher limits for thesecond polymer component, the blends of the second polymer component andthe first polymer component do not have the favorable tensile propertiesof the blends of the present invention. It is believed, while not meantto be limited thereby, the second polymer component needs to have theoptimum amount of isotactic polypropylene crystallinity to crystallizewith the first polymer component for the beneficial effects of thepresent invention. As discussed above, the preferred alpha-olefin isethylene.

The compositions of the present invention may comprise from about 5% toabout 98% by weight of the second polymer component. According to onepreferred embodiment, the compositions of the present invention maycomprise from about 30% to about 98% by weight of the second polymercomponent. Most preferably, the compositions of the present inventioncomprise from about 30% to about 95% by weight of the second polymercomponent.

Generally, without limiting in any way the scope of the invention, onemeans for carrying out a process of the present invention for theproduction of the copolymer second polymer component is as follows: (1)liquid propylene is introduced in a stirred-tank reactor, (2) thecatalyst system is introduced via nozzles in either the vapor or liquidphase, (3) feed ethylene gas is introduced either into the vapor phaseof the reactor, or sparged into the liquid phase as is well known in theart, (4) the reactor contains a liquid phase composed substantially ofpropylene, together with dissolved alpha-olefin, preferably ethylene,and a vapor phase containing vapors of all monomers, (5) the reactortemperature and pressure may be controlled via reflux of vaporizingpropylene (autorefrigeration), as well as by cooling coils, jackets,etc., (6) the polymerization rate is controlled by the concentration ofcatalyst, temperature, and (7) the ethylene (or other alpha-olefin)content of the polymer product is determined by the ratio of ethylene topropylene in the reactor, which is controlled by manipulating therelative feed rates of these components to the reactor.

For example, a typical polymerization process consists of apolymerization in the presence of a catalyst comprising a bis(cyclopentadienyl) metal compound and either 1) a non-coordinatingcompatible anion activator, or 2) an alumoxane activator. According toone embodiment of the invention, this comprises the steps of contactingethylene and propylene with a catalyst in a suitable polymerizationdiluent, said catalyst comprising, for example, according to a preferredembodiment, a chiral metallocene catalyst, e.g., a bis(cyclopentadienyl) metal compound, as described in U.S. Pat. No.5,198,401 which is herein incorporated by reference for purposes of U.S.practices and an activator. The activator used may be an alumoxaneactivator or a non-coordination compatible anion activator. Thealumoxane activator is preferably utilized in an amount to provide amolar aluminum to metallocene ratio of from about 1:1 to about 20,000:1or more. The non-coordinating compatible anion activator is preferablyutilized in an amount to provide a molar ratio of biscyclopentadienylmetal compound to non-coordinating anion of 10:1 to about 1:1. The abovepolymerization reaction is conducted by reacting such monomers in thepresence of such catalyst system at a temperature of from about −100° C.to about 300° C. for a time of from about 1 second to about 10 hours toproduce a copolymer having a weight average molecular weight of fromabout 5,000 or less to about 1,000,000 or more and a molecular weightdistribution of from about 1.8 to about 4.5.

While the process of the present invention includes utilizing a catalystsystem in the liquid phase (slurry, solution, suspension or bulk phaseor combination thereof), according to other embodiments, high pressurefluid phase or gas phase polymerization can also be utilized. Whenutilized in a gas phase, slurry phase or suspension phasepolymerization, the catalyst systems will preferably be supportedcatalyst systems. See, for example, U.S. Pat. No. 5,057,475 which isincorporated herein by reference for purposes of U.S. practice. Suchcatalyst systems can also include other well known additives such as,for example, scavengers. See, for example, U.S. Pat. No. 5,153,157 whichis incorporated herein by reference for purposes of U.S. practices.These processes may be employed without limitation of the type ofreaction vessels and the mode of conducting the polymerization. Asstated above, and while it is also true for systems utilizing asupported catalyst system, the liquid phase process comprises the stepsof contacting ethylene and propylene with the catalyst system in asuitable polymerization diluent and reacting the monomers in thepresence of the catalyst system for a time and at a temperaturesufficient to produce an ethylene-propylene copolymer of the desiredmolecular weight and composition.

It is understood in the context of the present invention that, in oneembodiment, more than one second polymer component may be used in asingle blend with a first polymer component. Each of the second polymercomponent components is described above and the number of second polymercomponent in this embodiment is less than three and more preferably,two. In this embodiment of the invention the second polymer componentsdiffer in the alpha-olefin content with one being in the range of 5 wt %to 9 wt % alpha-olefin while the other is in the range of 10 wt % to 22wt % alpha-olefin. The preferred alpha-olefin is ethylene. It isbelieved that the use of two second polymer component in conjunctionwith a single first polymer component leads to beneficial improvementsin the tensile-elongation properties of the blends.

The Blend of First and Second Polymer Components

The copolymer blends of first polymer component and second polymercomponent of the instant invention may be prepared by any procedure thatguarantees the intimate admixture of the components. For example, thecomponents can be combined by melt pressing the components together on aCarver press to a thickness of about 0.5 millimeter (20 mils) and atemperature of about 180° C., rolling up the resulting slab, folding theends together, and repeating the pressing, rolling, and foldingoperation about 10 times. Internal mixers are particularly useful forsolution or melt blending. Blending at a temperature of about 180° C. to240° C. in a Brabender Plastograph for about 1 to 20 minutes has beenfound satisfactory. Still another method that may be used for admixingthe components involves blending the polymers in a Banbury internalmixer above the flux temperature of all of the components, e.g., 180° C.for about 5 minutes. The complete admixture of the polymeric componentsis indicated by the narrowing of the crystallization and meltingtransitions characteristic of the polypropylene crystallinity of thecomponents to give a single or a small range crystallization and meltingpoints for the blend. These batch mixing procedures are typicallysupplanted by continuous mixing processes in the industry. Theseprocesses are well known in the art and include single and twin screwmixing extruders, static mixers for mixing molten polymer streams of lowviscosity, impingement mixers, as well as other machines and processes,designed to disperse the first polymer component and the second polymercomponent in intimate contact.

The polymer blends of the instant invention exhibit a remarkablecombination of desirable physical properties. The incorporation of aslittle as 5% first polymer component in the propylene/alpha-olefincopolymers increases the propylene sequence melting point or the polymersoftening point but, more significantly, reduces the range as comparedto the propylene/alpha-olefin copolymer. In addition, the incorporationof first polymer component in accordance with the instant inventionnearly eliminates the stickiness caused by the propylene/alpha-olefincopolymer. Further, the thermal characteristics of the copolymer blendsare markedly improved over those of the second polymer component whichis the propylene/alpha-olefin copolymers.

The crystallization temperature and the melting point of the blends arechanged as a result of the blending operation. In an embodiment of theinvention, the blend of first polymer component and second polymercomponent has single crystallization temperature and melting point.These temperatures are higher than the corresponding temperatures forthe second polymer component and close to that of the first polymercomponent. In other embodiments, the second polymer component and thefirst polymer component have distinct melting and crystallizationtemperatures but have these temperatures closer together than would beexpected for a combination of the second polymer component and the firstpolymer component. In all these cases the glass transition temperatureof the second polymer component is retained in the polymer blend. Thisfavorable combination of thermal properties permits their satisfactoryuse in injection molding operations without the orientation previouslyencountered. Injection molded articles prepared from the instantcopolymer blends accordingly exhibit excellent long term dimensionalstability. The advantages referred to above are obtained without theneed of elaborate purification of the propylene/alpha-olefin copolymeror the tedious preparation of a carefully structured block copolymer.Further, by the use of the second polymer component and the firstpolymer component, a blend can be obtained with a lower glass transitiontemperature than would be expected for a random copolymer of the samecomposition as the blend. In particular, the glass transitiontemperature of the blend is closer to that of the second polymercomponent and lower than the glass transition temperature of the firstpolymer component. This can be accomplished without an exceptionallyhigh alpha-olefin content in the polymer blend which we believe, whilenot meant to be limited thereby, would lead to degradation of thetensile-elongation properties of the blend.

The mechanism by which the desirable characteristics of the presentcopolymer blends are obtained is not fully understood. However, it isbelieved to involve a co-crystallization phenomenon between propylenesequences of similar stereoregularity in the various polymericcomponents, which results in one embodiment, a single crystallizationtemperature and a single melting temperature of the copolymer blendwhich is higher than those of the second polymer component which is thepropylene/alpha-olefin component of the blend. In another embodiment,the combination of the first polymer component and the second polymercomponent has a melting point closer together than would be expected ona comparison of the properties of the individual components alone. It issurprising that in the one embodiment, the blend has a singlecrystallization temperature and a single melting temperature, since itwould be expected by those skilled in the art that the blending of twocrystalline polymers would result in a double crystallizationtemperature as well as a double melting temperature reflecting the twopolymeric components. However, the intimate blending of the polymershaving the required crystallinity characteristics apparently results ina crystallization phenomenon that modifies the other physical propertiesof the propylene/alpha-olefin copolymer, thus measurably increasing itscommercial utility and range of applications.

While the above discussion has been limited to the description of theinvention in relation to having only components one and two, as will beevident to those skilled in the art, the polymer blend compositions ofthe present invention may comprise other additives. Various additivesmay be present in the composition of the invention to enhance a specificproperty or may be present as a result of processing of the individualcomponents. Additives which may be incorporated include, for example,fire retardants, antioxidants, plasticizers, and pigments. Otheradditives which may be employed to enhance properties includeantiblocking agents, coloring agents, stabilizers, and oxidative-,thermal-, and ultraviolet-light-inhibitors. Lubricants, mold releaseagents, nucleating agents, reinforcements, and fillers (includinggranular, fibrous, or powder-like) may also be employed. Nucleatingagents and fillers tend to improve rigidity of the article. The listdescribed herein is not intended to be inclusive of all types ofadditives which may be employed with the present invention. Upon readingthis disclosure, those of skill in the art will appreciate otheradditives may be employed to enhance properties of the composition. Asis understood by the skilled in the art, the polymer blend compositionsof the present invention may be modified to adjust the characteristicsof the blend as desired.

As used herein, Mooney Viscosity was measured as ML (1+4) at 125° C. inMooney units according to ASTM D1646.

The composition of Ethylene propylene copolymers, which are used ascomparative examples, was measured as ethylene Wt % according to ASTM D3900.

The composition of the second polymer component was measured as ethyleneWt % according to the following technique. A thin homogeneous film ofthe second polymer component, pressed at a temperature of about orgreater than 150° C. was mounted on a Perkin Elmer PE 1760 infra redspectrophotometer. A full spectrum of the sample from 600 cm-1 to 400cm-1 was recorded and the ethylene Wt % of the second polymer componentwas calculated according to Equation 1 as follows:ethylene Wt %=82.585−111.987X+30.045X ²wherein X is the ratio of the peak height at 1155 cm⁻¹ and peak heightat either 722 cm⁻¹ or 732 cm⁻¹, which ever is higher.

Techniques for determining the molecular weight (Mn and Mw) andmolecular weight distribution (MWD) are found in U.S. Pat. No. 4,540,753(Cozewith, Ju and Verstrate) (which is incorporated by reference hereinfor purposes of U.S. practices) and references cited therein and inMacromolecules, 1988, volume 21, p 3360 (Verstrate et al) (which isherein incorporated by reference for purposes of U.S. practice) andreferences cited therein.

The procedure for Differential Scanning Calorimetry is described asfollows. About 6 to 10 mg of a sheet of the polymer pressed atapproximately 200° C. to 230° C. is removed with a punch die. This isannealed at room temperature for 80 to 100 hours. At the end of thisperiod, the sample is placed in a Differential Scanning Calorimeter(Perkin Elmer 7 Series Thermal Analysis System) and cooled to about −50°C. to about −70° C. The sample is heated at 20° C./min to attain a finaltemperature of about 200° C. to about 220° C. The thermal output isrecorded as the area under the melting peak of the sample which istypically peaked at about 30° C. to about 175° C. and occurs between thetemperatures of about 0° C. and about 200° C. is measured in Joules as ameasure of the heat of fusion. The melting point is recorded as thetemperature of the greatest heat absorption within the range of meltingof the sample. Under these conditions, the melting point of the secondpolymer component and the heat of fusion is lower than the first polymercomponent as outlined in the description above.

Composition distribution of the second polymer component was measured asdescribed below. About 30 gms. of the second polymer component was cutinto small cubes about ⅛″ on the side. This is introduced into a thickwalled glass bottle closed with screw cap along with 50 mg ofIrganox1076, an antioxidant commercially available from Ciba—GeigyCorporation. Then, 425 ml of hexane (a principal mixture of normal andiso isomers) is added to the contents of the bottle and the sealedbottle is maintained at about 23° C. for 24 hours. At the end of thisperiod, the solution is decanted and the residue is treated withadditional hexane for an additional 24 hours. At the end of this period,the two hexane solutions are combined and evaporated to yield a residueof the polymer soluble at 23° C. To the residue is added sufficienthexane to bring the volume to 425 ml and the bottle is maintained atabout 31° C. for 24 hours in a covered circulating water bath. Thesoluble polymer is decanted and the additional amount of hexane is addedfor another 24 hours at about 31° C. prior to decanting. In this manner,fractions of the second polymer component soluble at 40° C., 48° C., 55°C. and 62° C. are obtained at temperature increases of approximately 8°C. between stages. Further, increases in temperature to 95° C. can beaccommodated, if heptane, instead of hexane, is used as the solvent forall temperatures above about 60° C. The soluble polymers are dried,weighed and analyzed for composition, as wt % ethylene content, by theIR technique described above. Soluble fractions obtained in the adjacenttemperature increases are the adjacent fractions in the specificationabove.

EPR in the data tables below is Vistalon 457, sold by the Exxon ChemicalCompany, Houston Tex.

The invention, while not meant to be limited thereby, is furtherillustrated by the following specific examples:

EXAMPLES Example 1 Ethylene/propylene Copolymerization to Form theSecond Polymer Component

Polymerizations were conducted in a 1 liter thermostatted continuousfeed stirred tank reactor using hexane as the solvent. Thepolymerization reactor was full of liquid. The residence time in thereactor was typically 7–9 minutes and the pressure was maintained at 400kpa. Hexane, ethene and propene were metered into a single stream andcooled before introduction into the bottom of the reactor. Solutions ofall reactants and polymerization catalysts were introduced continuouslyinto the reactor to initiate the exothermic polymerization. Temperatureof the reactor was maintained at 41° C. by changing the temperature ofthe hexane feed and by circulating water in the external jacket. For atypical polymerization, the temperature of feed was about 0° C.

Ethene was introduced at the rate of 45 gms/min and propene wasintroduced at the rate of 480 gms/min. The polymerization catalyst,dimethyl silyl bridged bis-indenyl Hafnium dimethyl activated 1:1 molarratio with N′,N′-Dimethyl anilinium-tetrakis(pentafluorophenyl)boratewas introduced at the rate of 0.00897 gms/hr. A dilute solution oftriisobutyl aluminum was introduced into the reactor as a scavenger ofcatalyst terminators: a rate of approximately 28.48 mol of scavenger permole of catalyst was adequate for this polymerization. After fiveresidence times of steady polymerization, a representative sample of thepolymer produced in this polymerization was collected. The solution ofthe polymer was withdrawn from the top, and then steam distilled toisolate the polymer. The rate of formation of the polymer was 285.6gms/hr. The polymer produced in this polymerization had an ethylenecontent of 13%, ML@125 (1+4) of 12.1 and had isotactic propylenesequences.

Variations in the composition of the polymer were obtained principallyby changing the ratio of ethene to propene. Molecular weight of thepolymer could be increased by a greater amount of ethene and propenecompared to the amount of the polymerization catalyst. Dienes such asnorbornene and vinyl norbornene could be incorporated into the polymerby adding them continuously during polymerization.

Example 2 Comparative Ethylene/propylene Polymerization where thePropylene Residues are Atactic

Polymerizations were conducted in a 1 liter thermostatted continuousfeed stirred tank reactor using hexane as the solvent. Thepolymerization reactor was full of liquid. The residence time in thereactor was typically 7–9 minutes and the pressure was maintained at 400kpa. Hexane, ethene and propene were metered into a single stream andcooled before introduction into the bottom of the reactor. Solutions ofall reactants and polymerization catalysts were introduced continuouslyinto the reactor to initiate the exothermic polymerization. Temperatureof the reactor was maintained at 45° C. by changing the temperature ofthe hexane feed and by using cooling water in the external reactorjacket. For a typical polymerization, the temperature of feed was about−10° C. Ethene was introduced at the rate of 45 gms/min and propene wasintroduced at the rate of 310 gms/min. The polymerization catalyst,dimethyl silyl bridged (tetramethylcyclopentadienyl) cyclododecylamidotitanium dimethyl activated 1:1 molar ratio with N′,N′-Dimethylanilinium-tetrakis(pentafluorophenyl)borate was introduced at the rateof 0.002780 gms/hr. A dilute solution of triisobutyl aluminum wasintroduced into the reactor as a scavenger of catalyst terminators: arate of approximately 36.8 mole per mole of catalyst was adequate forthis polymerization. After five residence times of steadypolymerization, a representative sample of the polymer produced in thispolymerization was collected. The solution of the polymer was withdrawnfrom the top, and then steam distilled to isolate the polymer. The rateof formation of the polymer was 258 gms/hr. The polymer produced in thispolymerization had an ethylene content of 14.1 wt %, ML@125 (1+4) of95.4.

Variations in the composition of the polymer were obtained principallyby changing the ratio of ethene to propene. Molecular weight of thepolymer could be increased by a greater amount of ethene and propenecompared to the amount of the polymerization catalyst. These polymersare described as aePP in the Tables below.

Example 3 Analysis and Solubility of Several Second Polymer Components

In the manner described in Example 1 above, several second polymercomponents of the above specification were synthesized. These aredescribed in the table below. Table 1 describes the results of the GPC,composition, ML and DSC analysis for the polymers.

TABLE 1 Melting (Mw) Ethylene Heat of Point ML (Mn) by by wt % fusion byDSC (1 + 4) @ 1 SPC GPC GPC by IR J/g (° C.) 25° C. SPC-1 102000 2489007.3 71.9 84.7 14 SPC-2 124700 265900 11.6 17.1 43.0 23.9 SPC-3 121900318900 16.4 7.8 42.2 33.1 SPC-4 11.1 25.73 63.4 34.5 SPC-5 14.7 13.247.8 38.4 Comparative Polymers EPR 47.8 not not 40 detected detectedaePP 11.7 not not 23 detected detectedTable 1: Analysis of the second polymer component and the comparativepolymers

Table 2 describes the solubility of the second polymer component

TABLE 2

Table 2: Solubility of fractions of the second polymer component. Sum ofthe fractions add up to slightly more than 100 due to imperfect dryingof the polymer fractions.

Table 3 describes the composition of the fractions of the second polymercomponent obtained in Table 2. Only fractions which have more than 4% ofthe total mass of the polymer have been analyzed for composition.

TABLE 3

Table 3: Composition of fractions of the second polymer componentobtained in Table 2. The experimental inaccuracy in determination of theethylene content is believed to about 0.4 wt % absolute

Example 4

A total of 72 g of a mixture of the first polymer component and thesecond polymer component, as shown in the Table 4, column 2, were mixedin a Brabender intensive mixture for 3 minutes at a temperaturecontrolled to be within 185° C. and 220° C. High shear roller bladeswere used for the mixing and approximately 0.4 g of Irganox-1076, anantioxidant available from the Novartis Corporation, was added to theblend. At the end of the mixing, the mixture was removed and pressed outinto a 6″×6″ mold into a pad 025″ thick at 215° C. for 3 to 5 minutes.At the end of this period, the pad was cooled and removed and allowed toanneal for 3 to 5 days. Test specimens of the required dumbbell geometrywere removed from this pad and evaluated on an Instron tester to producethe data shown in Table 4.

The first polymer component was Escorene 4292, a commercially availablehomoisotactic polypropylene from Exxon Chemical Company, Houston, Tex.The second polymer component was SPC-1 as characterized in Tables 1, 2and 3 above.

TABLE 4

Table 4: Stress versus extension (E) data for blends of first polymercomponent and second polymer component where the second polymercomponent is Component SPC-1 in the tables above. Shaded areas representbroken samples. Clear areas represent lack of data due to extensionbeyond machine limits.

Example 5

The first polymer component was Escorene 4292, a commercially availablehomoisotactic polypropylene from Exxon Chemical Company, Houston, Tex.The second polymer component was Component SPC-2 as characterized inTables 1, 2 and 3 above. These components were mixed in the same manneras described for Example 4.

TABLE 5

Table 5: Stress versus extension (E) data for blends of first polymercomponent and second polymer component where the second polymercomponent is component SPC-2 in the tables above. Shaded areas with nodata represent broken samples. Clear areas represent lack of data due toextension beyond machine limits.

Example 6

The first polymer component was Escorene 4292, a commercially availablehomoisotactic polypropylene from Exxon Chemical Company. The secondpolymer component was Component SPC-3 as characterized in Tables 1, 2and 3 above. These components were mixed in the same manner as describedfor Example 4.

TABLE 6

Table 6: Stress versus extension (E) data for blends of first polymercomponent and second polymer component where the second polymercomponent is Component SPC-3 in the tables above. Shaded areas with nodata represent broken samples. Clear areas represent lack of data due toextension beyond machine limits.

Example 7

The first polymer component was Escorene 4292, a commercially availablehomoisotactic polypropylene from Exxon Chemical Company, Houston, Tex.The second polymer component was Component SPC-4 as characterized inTables 1, 2 and 3 above. These components were mixed in the same manneras described for Example 4.

TABLE 7

Table 7: Stress versus extension (E) data for blends of first polymercomponent and second polymer component where the second polymercomponent is Component SPC-4 in the tables above. Shaded areas with nodata represent broken samples. Clear areas represent lack of data due toextension beyond machine limits.

Example 8

The first polymer component was Escorene 4292, a commercially availablehomoisotactic polypropylene from Exxon Chemical Company, Houston, Tex.The second polymer component was a mixture of Component SPC-1 andComponent SPC-5 as characterized in Tables 1, 2 and 3 above. Thesecomponents were mixed in the same manner as described for Example 4.

TABLE 8

Table 8: Stress versus extension (E) data for blends of first polymercomponent and EPR in the tables above. Shaded areas with no datarepresent broken samples.

Example 9 (Comparative)

The first polymer component was Escorene 4292, a commercially availablehomoisotactic polypropylene from Exxon Chemical Company, Houston, Tex.The second polymer component was Component EPR as characterized inTables 1, 2 and 3 above. These components were mixed in the same manneras described for Example 4.

TABLE 9

Table 9: Stress versus extension (E) data for blends of first polymercomponent and EPR in the tables above. Shaded areas with no datarepresent broken samples.

Example 10 (Comparative)

The first polymer component was Escorene 4292, a commercially availablehomoisotactic polypropylene from Exxon Chemical Company, Houston, Tex.The second polymer component was aePP as characterized in Tables 1, 2and 3 above. These components were mixed in the same manner as describedfor Example 4.

TABLE 10

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by thoseskilled in the art without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the scope of the claimsappended hereto be limited to the examples and descriptions set forthherein but rather that the claims be construed as encompassing all thefeatures of patentable novelty which reside in the present invention,including all features which would be treated as equivalents thereof bythose skilled in the art to which the invention pertains.

1. A process comprising: contacting propylene and ethylene in thepresence of a polymerization catalyst comprising a hafnium-containingcomposition under conditions effective to produce a polymer comprisingfrom about 7.3 to about 16.4 wt % ethylene and from about 83.6 to about92.7 wt % propylene, the polymer having a melting point of from about25° C. to about 90° C.
 2. The process according to claim 1 wherein thepolymer comprises from about 7.3 to about 14.7 wt % ethylene.
 3. Theprocess according to claim 2 wherein the polymer comprises from about7.3 to about 11.6 wt % ethylene.
 4. The process according to claim 3wherein the polymer comprises from about 7.3 to about 11.1 wt %ethylene.
 5. The process according to claim 1 wherein the polymercomprises from about 11.1 to about 16.4 wt % ethylene.
 6. The processaccording to claim 5 wherein the polymer comprises from about 11.1 toabout 14.7 wt % ethylene.
 7. The process according to claim 1 whereinthe polymer comprises from about 11.6 to about 16.4 wt % ethylene. 8.The process according to claim 7 wherein the polymer comprises fromabout 11.1 to about 14.7 wt % ethylene.
 9. The process according to anyof claims 1–8 wherein the polymer has a melting point from 42.2–84.7° C.10. The process according to claim 9 wherein the polymer has a meltingpoint from 43.0–84.7° C.
 11. The process according to claim 10 whereinthe polymer has a melting point from 43.0 to 63.4.
 12. The processaccording to claim 1 wherein the polymerization conditions comprise atemperature of from about −100° C. to about 300° C. for a time of fromabout 1 second to about 10 hours.
 13. The process according to claim 1comprising contacting the propylene and ethylene in the liquid phase.14. The process according to claim 13 wherein the liquid phase is asolution.
 15. The process according to claim 1 wherein thepolymerization catalyst is a metallocene catalyst.
 16. The processaccording to claim 15 wherein the metallocene catalyst comprises ahafnium-based bis (cyclopentadienyl) metal compound.
 17. The processaccording to claim 1 further comprising contacting the propylene andethylene in the presence of an activator.
 18. The process according toclaim 17 wherein the activator is an alumoxane.
 19. The processaccording to claim 17 wherein the activator is a non-coordinating anion.20. The process according to claim 1 further comprising combining thepolymer with an additive.
 21. The process according to claim 20 whereinthe additive is selected from fire retardants, antioxidants,plasticizers, pigments, antiblocking agents, coloring agents,lubricants, mold release agents, nucleating agents, reinforcements,fillers, stabilizers, and oxidative-, thermal-, andultraviolet-light-inhibitors.
 22. The process according to claim 1further comprising combining the polymer with a propylene-based polymerto form a polymer blend.
 23. The process according to claim 22 furthercomprising injection molding the blend to form an article.
 24. Asolution polymerization process comprising contacting propylene andethylene in the presence of (i) an activator and (ii) a polymerizationcatalyst comprising a hafnium-containing composition under conditionsincluding a temperature of from about −100° C. to about 300° C. for atime of from about 1 second to about 10 hours to produce a polymercomprising from about 7.3 to about 16.4 wt % ethylene and from about83.6 to about 93.7 wt % propylene, the polymer having: a melting pointof from about 42.2° C. to about 84.7° C.; a heat of fusion <75 J/g; acrystallinity of from about 2 to about 65% of homoisotacticpolypropylene; a MWD from about 1.8 to about 5.0.
 25. The processaccording to claim 24 wherein the polymer comprises from about 11.1 toabout 16.4 wt % ethylene.
 26. The process according to claim 24 whereinthe polymer has a melting point of from about 42.2° C. to about 63.4° C.27. The process according to claim 25 wherein the polymer has a meltingpoint of from about 42.2° C. to about 63.4° C.
 28. The process accordingto claim 24 wherein the polymer has a MWD of from about 2.0 to about3.2.
 29. The process according to claim 27 wherein the polymer has a MWDof from about 2.0 to about 3.2.